/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 25228
 * Date: 2024-09-30
 * Time: 19:02
 */
import java.util.Scanner;

public class Main5{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        double v0 = in.nextDouble();
        double v1 = in.nextDouble();
        int t = in.nextInt();
        AccelerationCal ac = new AccelerationCal();
        double acceleration = ac.calAcceleration(v0, v1, t);
        System.out.println(acceleration);
    }
}


class AccelerationCal
{
    public double calAcceleration(double v0, double v1, int t){
        return (v1-v0)/t;
    }
}


